The content of radicals in the base polymer film before and after grafting is an important issue in theproduction and use of membranes for electrochemical devices by radiation grafting. In this work a methodhas been developed for determination of relative radical content in fluoropolymer films using MgO asinternal standard. It has been demonstrated that peroxy radicals generated by electron irradiation of ETFEdecay rapidly within the first day after the irradiation, probably due to recombination within the amorphousdomains. The extent of decay can be reduced by lowering the storage temperature which decreases polymerchain mobility. At room temperature decay of radicals in the crystallites too is indicated, although at a lowerrate. In order to obtain reasonable grafting yield storage should therefore be as short or cold as possible. Allradicals have been found to disappear in the grafting process, and no significant amount of potentiallyharmful radicals is thus left in the final membrane.